The forklift is a basic tool of today's industry, but not only: warehouses, distribution centres, manufacturing plants, factories, and many other commercial and agricultural applications depend on forklifts utilization to keep the daily work running easily. Forklifts are named for the L-shaped “forks” typically used to handle and to lift pallets, but the trucks can be outfitted with different accessories for picking up spools, drums, or other specific loads as well. These trucks, also called “lift trucks”, are available for both indoor and outdoor applications.
A lift truck is typically designed and includes the components as follows. The whole truck is a motive machine with wheels powered through a transmission and drive train. An engine is provided, for example a diesel or a gas powered internal combustion engine, or a battery-powered electric motor. A counter balance is attached to the rear of the machine, which is a heavy iron mass, necessary to compensate for the load handled. In an electric forklift the battery may serve also as a counterweight. Most important, the lift-truck includes a mast, which is the vertical assembly responsible for raising or lowering a load. A fork lift mast is made up of interlocking rails necessary to provide lateral stability. These rails or guideway structures are guided by rollers or bushings.
Depending on the application, typically some configurations are possible:                single stage or “free lift” movement: the height of the forks can be raised before the mast extension;        2 stages (duplex). The mast has two sections, one outer that doesn't move (fixed mast structure) and one inner (movable mast structure) that raises and elevates the carriage and forks;        3 stages (triplex). It consists of three sections (one outer, fixed and two inner rails, movable). The two inner sections raise from outside to inside as the mast raises.        
The mast is hydraulically operated and consists of cylinders and interlocking rails for lifting and lowering operations. Further, forks are provided, which are the L-shaped members that engage the load. The rear vertical portions of the forks are attached to a carriage and the front horizontal portions are inserted into or under the load, usually a pallet. Finally, a cabin with a seat for the operator is provided with pedals and switches for controlling the whole machine functions.
Usually the lift of the loads is performed by means of a hydraulic actuator. A hydraulic electro-pump supplies pressurized fluid (oil) to an hydraulic circuit (pipes, valves, distributors, actuators) to compose a system which also lifts the load by means of hydraulic cylinder. However, the efficiency of such hydraulic system is low. According to the hydraulic solution an estimate of the efficiency is related to the efficiency of the following components:
Electro pump motor: 80%, Hydraulic pump: 85%, Hydraulic valve: 90%, Hoses: 95%, Hydraulic piston: 90%. This gives a total efficiency of η=0.8×0.85×0.9×0.95×0.9=0.52 corresponding to 52%.